Density and pressure in fluids
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why snow shoes work
- Density
Read the transcript of the teaching part
Last time
Before we start: last time, in Drag, viscous forces and terminal velocity, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why snow shoes work
A walker in deep snow sinks to the knees, but in snow shoes she stays on top. Her weight has not changed. What has changed is the area it is spread over, and the pressure is the force per unit area.
Density
Density is mass per unit volume: rho equals m over V. The SI unit is kilogram per cubic metre. Other units such as microgram per cubic millimetre are valid, but not newton per cubic metre. A solid with mass two kilograms and volume two hundred and fifty cubic centimetres has density eight thousand kilograms per cubic metre. Quote density as mass per unit volume, never as mass of a cubic metre.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Density · Pressure in fluids · Pressure.
The whole chapter: Forces, Density and Pressure, Forces, Density and Pressure.
Chapter 4.2: Matter
- Density and pressure in fluids 6 min
- Upthrust and flotation 5 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.